The field of the invention is treatment of eye disorders, and more particularly setons used to treat uncontrolled intraocular pressure.
Glaucoma is a disease of the eye which affects a substantial number of people. It involves uncontrolled intraocular pressure within the eye which is typically caused by obstruction of the trabecular meshwork. The disease is serious since it often results in permanent damage to the optic nerve. Surgical treatment of glaucoma has been limited due to failure to control intraocular pressure as well as post-operative complications which tend to exacerbate the pre-operative conditions.
The eye is a complex part of the body. In general terms, the outer surface of the eye is covered with a thin filmy layer known as the conjunctiva. The conjunctiva is adjacent to the cornea and, among other things, serves to produce tears which protects the cornea from exposure to the outside environment. The tissue surrounding the eye is known as sclera.
The cornea acts to refract light through the area behind the cornea, known as the anterior chamber, and towards the lens. The size of the entrance aperture of the eye, known as the pupil, is controlled by muscles within the eye. The iris is positioned behind the anterior chamber and acts to permit the eye to focus on objects which are close or far away.
The retina is positioned in the back of the eye; the remaining portion of the eye behind the lens and iris being known as the vitreous chamber. The lens acts to focus the light coming from the pupil, through the vitreous chamber and onto the retina where the images are processed by the brain.
The fluid within the eye, known as aqueous humor or aqueous, is produced by the ciliary body and normally migrates through the pupil and into the anterior chamber where it is communicated through the trabecular meshwork and into the aqueous veins, which form fluid collection channels beneath the conjunctiva. Glaucoma results when the intraocular pressure is not relieved by the above-described normal aqueous migration.
Medical treatment of the uncontrolled high pressure of glaucoma has had varying success. Medicines in the form of eye drops or pills act to reduce the production of aqueous in the ciliary body and/or increase the outflow of aqueous through the trabecular meshwork are often used. Doctors have also attempted to treat glaucoma through what are generally known as surgical filtration procedures. One such technique creates a hole through the limbus under the sclera and excises a piece of the trabecular meshwork (trabeculectomy). After such filtration surgery, the aqueous is supposed to flow from the anterior chamber through the excised surgical area and into the space beneath the conjunctiva and sclera where it is finally absorbed by the body.
Another surgical technique to attempt to improve the filtration through the trabecular meshwork involves placing several Argon laser burns throughout the entire circumference of the trabecular meshwork in hopes of opening up the trabecular meshwork spaces. This procedure is called Argon laser trabeculoplasty.
In certain high risk cases, the above-described surgical techniques are typically unsuccessful due to the post-operative scarring of the wound or the scleral tissue. This scarring prevents migration of the aqueous out of the eye and results in a recurrence of the uncontrolled intraocular pressure of glaucoma.
Another attempt to relieve the uncontrolled high pressure of glaucoma is to perform what is known as an iridencleisis. The procedure involves pulling a piece of the iris through the wound from the anterior chamber to lie under the sclera and conjunctiva. Serious infection and inflammation of the wound often results from this procedure.
An additional technique implants a piece of cartilage into the eye. This procedure typically fails due to the formation of scar tissue about the wound resulting in the total closure of the wound which prevents the migration of aqueous.
Finally, seton implants in the form of polypropylene tubing and a device known as a Krupin Valve implant have failed due to post-operative extrusion of the implants through the wound as well as the formation of blood and fibrin clots and scar tissue in the area of implantation which act to inhibit the flow of aqueous. In addition, where the seton material is not biocompatible with the eye, serious infection, biological rejection and the formation of scar tissue typically prevent such seton implants from being successful.
In cases where medicines, laser trabeculoplasty and surgical filtration procedures, such as a trabeculectomy, have failed, the only medically proven method for controlling pressure within the eye is to permanently damage the ciliary body, i.e. the part of the eye which produces the aqueous. This procedure, known as Cyclocryotherapy, involves externally freezing the sclera above the ciliary body. This process kills the ciliary body and, in addition, eradicates all functioning or potentially functioning trabecular meshwork in the area and is fraught with complications including bleeding within the eye and raises a significant risk of total loss of use of the eye.